EXTjs comobox tpl not working In IE11

Question

I am new to Ext JS. I am working in one of the new project where it is using extjs extensively .One of the EXTjs code snippet is working fine in browsers MS edge, Chrome and Firefox but not in IE 11 . It looks strange . Please find my snippet below

  ${comboVar} = new Ext.form.ComboBox({
                    id : '${comboId}',
                    allowBlank: false,
                    minLength: 1,
                    maxLength:200,
                    invalidClass: '',
                    blankText: '',
                    invalidText: '',
                    transform : '${comboId}',
                    disableKeyFilter : true,
                    mode : 'local',
                    autoHeight : true,
                    resizable : true,
                    listWidth : 310,
                    width : 313,
                    triggerAction : 'all',
                    emptyText : '<fmt:message key="editTransition.selectStageHint" bundle="${messages}"/>',
                    tpl: '<tpl for="."><div class="x-combo-list-item">{text:htmlEncode}</div></tpl>'
                });

When I remove tpl config and changing 'new Ext.form.ComboBox' to 'new Ext4.form.ComboBox' (changing version to 4) . This is working but still have some side effects (validation is not working ).

Can any one help me to understand why the above code snippet is not working In IE11 and why it is started to work when I remove TPL and changed the Extjs version to 4.

My application is using both Ext3.4 and Ext4.2.0. So it have exposes to both the object Ext and Ext4.